The present invention relates to a regenerative heat engine. More particularly, the present invention relates to a minature heat engine which is designed to produce power for the operation of equipment such as an artificial heart.
In the operation of power sources for equipment such as artificial heart pumps in which continuous operation is critical, previous sources of power have been characterized by many inherent disadvantages, including excessive size and weight, inefficiency, poor reliability, and equipment complexity which have made difficult the process of assembly and disassembly. Additional drawbacks to such prior art power sources have included the necessity for providing electric power input at relatively short intervals and the build-up of heat around the power source which has precluded installation in or near the body of the patient.
By the present invention there is provided a power source for the operation of equipment such as an artificial heart in which the previously mentioned disadvantages have been overcome, the power source being in the form of a miniature regenerative heat engine. It is well known that Stirling engines (regenerative engines) possess certain advantages over the more widely used internal combustion engines, including quiet operation, potentially high efficiency and adaptability to the use of any of a large number of sources of heat including liquids, gases, solids, waste heat, electrically supplied heat and solar radiation. Stirling engines also require no ignition system, nor are carburetors or fuel injectors required, while relatively low speed operation can be employed. The many other advantages inherent in regenerative engines are well known to those skilled in the art. The Ideal Stirling cycle is characterized by isothermal compression followed by an addition of heat at constant volume from a regenerator, then an isothermal expansion, and finally a constant volume removal of heat for storage in the regenerator.
The regenerative cycle employed in the present invention is characterized by four sequential processes.
1. Heat leaves the regenerator and enters the gas at constant engine gas volume. Engine pressure rises. PA1 2. Heat leaves the regenerator and enters the gas at constant pressure. Gas is expelled from the engine through a check valve into the high pressure reservoir. PA1 3. Heat leaves the gas and enters the regenerator at constant engine gas volume. Engine pressure falls. PA1 4. Heat leaves the gas and enters the regenerator at constant engine gas pressure. Gas returns to the engine through a check valve from the low pressure reservoir.
The present heat engine features increased reliability and efficiency, as well as ease of assembly and disassembly, and is capable of using heat supplied from various sources, including electric or radio isotope heat. The power output of the present heat engine is fully controllable. Preassembled inlet and outlet check valve modules are incorporated in the engine and a permanently sealed vacuum insulation package is maintained separate from the engine. Also incorporated in the engine is a thermal energy storage package so that the engine can operate for extended periods without power input. A temperature control heat pipe is installed to conduct any excess heat away from the hot end of the engine while a temperature distribution heat pipe is installed as a jacket around the heat source in order to distribute heat evenly over the hot end of the engine. Additional features of the present engine include a flexural support to support and guide the displacer at the hot end and a metal bellows seal for sealing off the displacer drive from the remainder of the engine.